Consolidate Linux recv implementation

This patch consolidates the recv Linux syscall implementation on
sysdeps/unix/sysv/linux/recv.c.  The changes are:

  1. Remove recv from auto-generation syscalls.list on the architecture
     that uses __NR_recv.
  2. Define __NR_recv for architectures that supports it.  It was done
     instead of defining in default kernel-features.h because current Linux
     practice for new ports is to implement only __NR_recvfrom [1] and it will
     require adding new kernel-features for ports that do not require it
     (aarch64 for instance).
  3. Remove __ASSUME_RECVFROM_FOR_RECV_SYSCALL and decide to use
     __NR_recvfrom for recv generation based on __ASSUME_RECVFROM_SYSCALL.

Checked on i686-linux-gnu, x86_64-linux-gnu, x86_64-linux-gnux32,
aarch64-linux-gnu, arm-linux-gnueabihf, and powerpc64le-linux-gnu.

	* sysdeps/unix/sysv/linux/alpha/syscalls.list: Remove recv from
	auto-generation list.
	* sysdeps/unix/sysv/linux/arm/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/hppa/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/ia64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/mips/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/alpha/kernel-features.h
	(__ASSUME_RECV_SYSCALL): New define.
	* sysdeps/unix/sysv/linux/arm/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/hppa/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/ia64/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/mips/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/i386/kernel-features.h
	(__ASSUME_RECVFROM_FOR_RECV_SYSCALL): Remove define.
	* sysdeps/unix/sysv/linux/m68k/kernel-features.h
	(__ASSUME_RECVFROM_FOR_RECV_SYSCALL): Remove define.
	* sysdeps/unix/sysv/linux/s390/kernel-features.h
	(__ASSUME_RECVFROM_FOR_RECV_SYSCALL): Remove define.
	* sysdeps/unix/sysv/linux/generic/recv.c: Remove file.
	* sysdeps/unix/sysv/linux/mips/mips64/recv.c: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/recv.c: Likewise.
	* sysdeps/unix/sysv/linux/recv.c: Simplify includes.
	(__libc_recv): Use __ASSUME_RECVFROM_SYSCALL instead of
	__ASSUME_RECVFROM_FOR_RECV_SYSCALL to issue recvfrom syscall.

[1] include/asm-generic/unistd.h (__ARCH_WANT_SYSCALL_DEPRECATED)